Method of preparing unsaturated aldehydes and acids



United States Patent US. Cl. 260-533 9 Claims ABSTRACT OF THE DISCLOSURE Unsaturated acids and aldehydes are prepared by re-"- acting propylene and isobutylene with oxygen at an elevated temperature in the presence of a catalyst containing molybdenum oxide, tellurium oxide and a bismuth or antimony phosphate to form acrolein and acrylic acid, and methacrolein and methacrylic acid.

This invention relates to new and useful catalysts and to a method of preparing unsaturated aldehydes and unsaturated carboxylic acids by oxidation of unsaturated hydrocarbons at an elevated temperature, and relates more particularly to catalysts comprising a mixture of a molybdenum oxide, tellurium oxide and a bismuth or antimony phosphate in a molar ratio of 100 M00 100 TeO and 10-100 of a bismuth or antimony phosphate and to a method of preparing acrolein and acrylic acid or methacrolein and methacrylic acid by passing vapors of propylene or isobutylene and an oxygen-containing gas over the catalyst at a temperature of from about 325 C. to about 550 C. The catalyst can also be designated as wherein M is Bi or Sb and with the P being in the form of a phosphate i.e., each P is attached to 3 or 4 oxygen atoms.

Numerous attempts have been made in the past to prepare products of higher oxidation state from hydrocarbons, especially from the normally gaseous hydrocarbons. However, all prior catalysts and procedures for oxidizing monoolefinic gaseous hydrocarbons to monoolefinically unsaturated aldehydes or monoolefinically unsaturated carboxylic acids with the same number of carbon atoms as the hydrocarbon having serious shortcomings. The catalysts either have a very short active life, or they convert only a portion of the hydrocarbon to desired end groups per pass; they oxidize the hydrocarbon excessively to form high proportions of carbon monoxide or carbon dioxide or both; they are not sufficiently selective, so that the hydrocarbon molecule is attacked at both the olefinic unsaturation and at a methyl group; or the oxidation of the olefin does not proceed beyond the aldehyde stage.

It is therefore unexpected to find a catalyst having unusually long life that will convert a substantial amount, more than 50% per pass, of a gaseous monoolefin such as propylene or isobutylene to yield very high proportions of acrolein and acrylic acid or methacrolein and methacrylic acid. It is also unexpected to find a catalyst that produces a wide range of ratios of olefinic aldehyde to monoolefinically unsaturated carboxylic acid by controllable changes in reaction conditions or catalyst composition. Mol percent efiiciencies of about 16 to 50 for the aldehyde and about 32 to 40 for the unsaturated carboxylic acid have been obtained with the catalyst and process of this invention.

The reactants The essential reactants are (1) propylene or isobutyl- 3,467,700 Patented Sept. 16, 1969 ene and (2) an oxygen-containing gas, which can be pure oxygen, oxygen diluted with an inert gas, oxygen enriched air or air without additional oxygen. For reasons of economy, air is the preferred oxygen-containing reactant.

For the purpose of this invention the hydrocarbons which are oxidized can be defined generically by the formula wherein it is also apparent that the end products formed result from the oxidation of only one methyl group on the hydrocarbon molecule while the terminal remains intact.

Stoichiometric ratios of oxygen to olefin for the purpose of this invention are 1.5 to 1. Slightly lower amounts of oxygen can be used at a sacrifice of yield. It is preferred, however, to use 33 to 66% excess oxygen. Larger excesses do not impair the yields of aldehydes and acids, but for practical considerations an excess much above would require extremely large equipment for a given production capacity.

The addition of steam into the reactor along with the hydrocarbon and oxygen-containing gas is desirable but not absolutely essential. The function of steam is not clear, but it seems to reduce the amount of carbon monoxide and dioxide in the efiiuent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbons such as propane are rather inert under the reaction conditions. Nitrogen or other known inert gases can be used as diluents if desired.

The catalyst and its preparation There are several methods for the preparation of the catalyst, which can be supported or unsupported. It is possible to dissolve each of the starting ingredients in water and combine them from the aqueous solutions or the ingredients can be dry blended. Because of the more uniform blend obtained by the solution procedure, it is preferred.

A general procedure for preparing a catalyst from water-soluble ingredients is to dissolve the requisite amount of a molybdenum salt, a tellurium salt and a bismuth-or antimony salt in water. Add the requisite amount of phosphoric acid to the bismuth or antimony salt solution. Add the tellurium salt solution to the molybdenum salt solution and then add the bismuth or antimony salt phosphoric acid mixture to the molybdenumtellurium salt mixture. The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding a dry support or an aqueous slurry thereof to the aqueous solution of catalyst or the aqueous catalyst ingredients can be added to the slurry of the support.

Alternatively, a slurry of the catalyst ingredients can be prepared in water, then dried and baked. For supported catalysts the aqueous slurry of the catalyst ingredients can be added to an aqueous suspension of the support or vice versa, and then dried and baked.

Another method is to blend the dry ingredients of the desired particle size and then mix them thoroughly. Thorough blending and uniform particle size is desired.

A specific example of the solution method is now set forth.

In this procedure the ingredients are precipitated on blending.

(a) Dissolve 105.96 g. of ammonium molybdate in 300 ml. of distilled water,

(b) Dissolve 31.922 g. of TeO in 80 ml. of concentrated HCl.

Add the tellurium salt solution to the ammonium molybdate solution. A precipitate forms.

(c) Dissolve 133.4 g. of BiCl in water and add 46.2 g. of 85% H PO Add this mixture slowly to the precipitated ammonium molybdate-Te mixture.

Dry on a steam bath and bake for 16 hours at 400 C. Thereafter, the catalyst is ground to the desired mesh size and sieved. For supported catalysts an aqueous slurry .4 obtained with molar ratios of about 3 to 5 per mol of olefin and for this reason are preferred.

The contact time can vary considerably in the range of about 2 to 70 seconds. Best results are obtained in a range of about 8 to 54 seconds and this range is preferred. Longer contact times usually favor the production of acid at any given temperature.

The particle size of catalyst for fixed bed operations used is from 10-18 mesh. As is known, for fixed beds, the size may be of a wider range particle size. For fluid-bed 10 of the support can be added to the catalyst ingredients, or systems the catalyst size should be from 80-325 mesh vice versa, prior to drying and baking. (U.S. Sieve).

A supported catalyst may be prepared by adding to The reaction can be run at atmospheric pressure, in (c) 240 grams of an aqueous colloidal dispersion of a Partial Vacuum Under induced Pressure "P to microspheroidal silica in a concentration of 30-35% SiO 100 p.s.i. Atmospheric pressure is preferred for fixed-bed (Ludox H.S.). The silica may also be added to one of systems and a pressure of 1 to 100 p.s.i. for fluid-bed the individual ingredients or (c) added to the silica disreactions. Operation at a pressure which is below the dew persion. point of the unsaturated acid at the reaction temperature Among the suitable supports are silica, silica containis advantageous. ing materials, such as diatomaceous earth, kieselguhr, The data in the examples show that wide variations in silicon carbide, clay, aluminum oxides and even carbon, Percentages of unsaturated acids and aldehydes can be although the latter tends to be consumed during the reac- Obtained With a Single Catalyst, using fixed ratio reaction tants but changing the temperature and/or contact time.

Th ct h i l str t of th catalysts d Further variation is obtainable by controlling the other by the above procedures is not known, but catalysts with variables in the reaction including the catalyst composimolar ratios of 100 Mo, 10-100 Te and 10-100 of a tions Within the limits set f h hereinbismuth or antimony phosphate can be used for oxidizing The examples are intended to illustrate the invention the monoolefinic hydrocarbon to aldehyde and/or carbut n to limit it. boxylic acid. The catalyst contains chemically bound oxy- The xamples gen so that the generic formula can be Written as A series of runs was made in a fixed-bed reactor of a high silica (Vyeor) glass tube 12 inches long and 30 310o 210-100 4( 2 7 3 mm. outer diameter. The reactor had three inlets, one for air, one for steam and one for propylene. Three or bismuth or other phosphate1n 1no- The Phosphate can external electrically operated heating coils were wound be 3 4 radical, PY P P r Of a P YP P on the reactor. One of the coils extended along the entire length of the reactor and each of the remaining coils ex- Reactlon condltlons tended only about one-half the length of the reactor.

The reaction can be carried out in either a fixed Outlet vapors were passed through a short water cooled fluidized catalyst bed 40 condenser. Uncondensed gases were passed through a gas The reaction temperature can range from about 300 to fhromatogfaph g i f model 154D) and 475 C. for the oxidation of propylene but the preferred yzgdthcontmuous The i co.ndensate T range is from about 325 to about 450 C. Below 325 C. 22 g ggggg for acry 1c acld and acmlem m the the conversion r ass is lower and low temperature tends to produce moib aldehyde than desired. Usually, a reactor was filled to about 90% of i capaclty longer contact time is needed at lower temperatures to 211th g of a qatalyst P i Sohmon method obtain the yields of desired products obtainable at higher 3 2,? fi ahratlo 0 75 T602 and temperatures. Above 450 C. in the propylene oxidation B1 mpmca y t e cata yst some of the desired end products appear to be oxidized Mo Te Bi P o to carbon oxides. For isobutylene, oxidation temperatures and the P is Present as P04. The catalyst was not gg fi gig are deslrable the Preferred range bemg ported and had a mesh size of 1048 (US. Sieve).

' Steam at a temperature of ZOO-250 C. was first passed The molar who of oxygen 10 P py lsobuQlene into the reactor. Then propylene and air were separately should be at least 2 to 1 for good conversion and yields. H f d into h stream of water vapor This mixture than soffle eXeeSS Q y 33 to 66 11191 P eh even m e passed through a pre-heater and entered the reactor at desirable and is preferred. There is no critical upper limit about 200450 C The reactor was preheated to about as to the amount of oxygen, but when air 1s used as the 2 5 before h gas f d was begun oxygeh-eehtfllhlng g It becomes pp f too great The ratio of reactants was about 2.955 mols of oxygen f excess W111 q l f large feeders, p p gr cOIIlplesS- and 4.36 mols of steam per mol of propylene. Cold con- 8 f Othel' allXlherY q P for y given tact time was varied as shown in the table below. of desired end product. It 15 therefore best to limit the Th ti temperature was i d as h reaction amount of air to provide a 33 to 66% excess of oxygen. proceeded,

This range provides the largest proportion of acid, under The table below summarizes the data obtained in these given reaction conditions. Also, since care is needed to runs:

M01 Molperccnt yield on M01 percent Contact percent propylene converted elficieucy Run To1np., time, propylene No. 0. seconds converted Acr. AA Acr. AA

Acr.=Acrolein; AA=Acrylic Acid.

avoid an explosive mixture, the limiting of air aids in that direction.

The molar ratio of steam to propylene or isobutylene 75 can range from 0 to about 5 to 7, but best results are For another series of runs an antimony catalyst was prepared as follows:

(a) 105.96 g. of ammonium molybdate was dissolved in ml. of distilled water at about 50 C.

(b) 31.922 g. TeO was dissolved in 80 ml. of concentrated HCl.

The tellurium salt solution was added to the ammonium molybdate solution. A precipitate formed.

91.24 g. SbCl was dissolved in water and 69.2 g. of 85% H PO added. This mixture was added slowly to the precipitated ammonium molybdate-TeO mixture.

The mixture was dried on a steam bath and baked for 16 hours at 400 C. Thereafter, the catalyst was ground to -18 mesh size and sieved.

The reactor was filled to about 90% of its capacity with 170 ml. of this catalyst having a ratio of 75 M00 25 TeO and 12.15 Sb (P O Empirically the catalyst is and the P is present as P 0 The catalyst was not supported and had a mesh size of 10-18 (U.S. Sieve).

Steam at a temperature of 200250 C. was first passed into the reactor. Then propylene and air were separately fed into the stream of water vapor. This mixture then passed through a pre-heater and entered the reactor at about 200-250 C. The reactor was pre-heated to about 285 C. before the gas feed was begun.

The ratio of reactants was about 2.955 mols of oxygen and 4.36 mols of steam per mol of propylene. Cold contact time was 45 seconds.

The reaction temperature was varied as the reaction proceeded.

The table below summarizes the data obtained in these runs:

* Mel Mel percent yield on percent propylene converted Temp propylene Run N 0 C converted Aer. AA

Acr=Acrolein; AA =Aerylic Acid.

I claim:

1. A method of preparing a mixture of unsubstituted monoolefinic aldehydes and monoolefinic monocarboxvlic acids by oxidation of a methyl group of a hydrocarbon having the structure comprising passing over a catalyst a mixture of gases having a molar ratio of 1 mol of said monoolefinic hydrocarbon, an oxygen containing gas containing about 1.5 to 4 mols of oxygen and up to 7 mols of water vapor per mol of said monoolefinic hydrocarbon, at a temperature of from about 300 C. to about 500 C., the said catalyst consisting essentially on a molar basis, of

wherein M is Bi or Sb and in which each P is combined with 3 to 4 atoms of oxygen and the M to P ratio ranges from 1M to 1P to 4M to 6P.

2. A method of preparing a mixture of acrolein and acrylic acid comprising passing a mixture of propylene,

and an oxygen containing gas containing from about 1.5 to 4 mols of oxygen per mol of propylene over a catalyst having the empirical formula wherein M is Bi or Sb and in which each P atom is combined with 3 to 4 atoms of oxygen and the M to P ratio ranges from 1M to 1P to 4M to 6P, at a temperature of from about 325 C. to about 450 C.

3. The method of claim 2 in which the M to P ratio is 2.0 to 1 to l.

4. The method of claim 2 wherein the catalyst contains a major proportion of M00 and smaller proportions of TeO and (Sb).;(P O in a molar ratio of M00 10-100 TeO and 10-100 (Sb) (P O 5. The method of claim 2 wherein the catalyst contains a major proportion of M00 and smaller proportions of TeO and BiPO in a molar ratio of 100 M00 10-100 TeO and 10l00 BiPO 6. A method of preparing a mixture of acrolein and acrylic acid comprising passing a mixture of propylene, an oxygen containing gas containing from about 1.5 mols of oxygen per mol of propylene and up to 7 mols of water vapor per mol of propylene through a bed of a catalyst consisting essentially of in which the P is present as P 0 at a temperature of from about 360 C. to about 425 C.

7. A method of preparing a mixture of methacrolein and methacrylic acid comprising passing a mixture of isobutylene and an oxygen containing gas in an amount sufficient to provide from about 1.5 to about 3 mols of oxygen per mol of isobutylene, through a bed of a catalyst consisting essentially of wherein M is Bi or Sb and in which the M to P ratio ranges from M to P to M to P and in which each P is combined with 3 to 4 atoms of oxygen.

8. The method of claim 7 wherein the catalyst contains M00 Te0 and (Sb) (P O in a molar ratio of 100 M00 10-100 Te0 and 10-100 (Sb) (P O 9. The method of claim 7 wherein the catalyst contains M00 TeO and BiPO in a molar ratio of 100 M00 10-100 TeO and 10-100 BiPO References Cited UNITED STATES PATENTS 2,941,007 6/1960 Callahan et al 260533 X 3,192,259 6/1965 Fetterly et al. 260533 FOREIGN PATENTS 839,808 6/1960 Great Britain. 878,802 10/1961 Great Britain. 903,034 8/ 1962 Great Britain.

LORRAINE A. WEINBERGER, Primary Examiner D. STENZEL, Assistant Examiner US. Cl. X.R. 252437; 260604 

